This invention relates to apparatus for retaining small drops of liquid samples, for purposes of analysis and, more particularly, to such apparatus that is designed to replace conventional microtitration plates of the type having plural microwells, which plates normally are used in a conventional microtitration plate support provided in, for example, microplate readers, sample-loaders, and the like.
The chemical and biological analyses of various liquid samples have been facilitated by equipment which now has become conventional. Such equipment includes spectrophotometric systems that are manually or automatically operated to provide spectroanalysis of such liquid samples, and loading apparatus for introducing those samples into microwells. These systems are commercially available from, for example, Bio-Tek Instruments Inc. of Burlington, Vt., Models EL307, EL308 and EL3l0 microplate readers; Bio-Rad Laboratories, Model 2550 EIA microtitration plate reader; Dynatech Laboratories, Inc. of Alexandria, Va., Models Mini Reader II, Micro Fluor and microsample loading apparatus Models Dynadrop SR, Autopipetter and Rotatiter. The aforementioned equipment cooperates with microtitration plates which, generally, are of plastic material, are of generally rectangular configuration and are integrally formed with an array of so-called microwells, each storing a liquid sample for analysis.
Such microtitration plates are useful in measuring the presence, type and quantity of, for example, biological and biochemical entities. Conventional microtitration plates typically are used in the measurement of specific proteins, such as antigens, antibodies, enzymes, hormones, etc. Such microtitration plates have an array of microwells, such as 96 microwells arranged in an 8.times.12 array, each microwell being loaded with a liquid sample on the order of about 100-200 microliters (.mu.l) of sample or reagent. The sample contained in one of more of such microwells is analyzed by the relative positioning of that microwell with respect to, for example, the reading head of the aforementioned readers. Samples in successive or selected ones of such microwells may be analyzed in rapid order.
However, although such conventional microtitration plates are used widely in several applications, and although several reading and sample-loading devices compatible with such microtitration plates are available, various disadvantages and drawbacks are associated with such microtitration plates. For example, the quantity of liquid sample that must be contained by each microwell (on the order of about 200 .mu.l) is sufficiently large that, in some instances, the total quantity of sample that is available for analysis may be inadequate for satisfactory use with such microwells. Also, the time required to perform each analysis including loading the requisite number of microwells with liquid sample prior to analysis thereof, and the time needed to empty and test-wash such microwells is quite high. This significant delay is a key factor in the overall time needed to analyze such liquid samples and a serious drawback in the use of conventional microtitration plates.
Another disadvantage associated with conventional microtitration plates is the need for large storage space to accommodate a sufficient supply of the relatively large microtitration plates. Also, the ability to utilize only a small portion of the microtitration plate for successive analyses is possible but cumbersome. The present invention has resolved these problems.
Yet another disadvantage attending conventional microtitration plates is the difficulty in observing, for example, by simple light microscopy any biological particulate substance that may or may not be adhering to the walls of a microwell. Since such walls generally are disposed non-perpendicular to the light path of a conventional microscope, particles that might adhere thereto are not easily seen because the path of the light beam generally does not impinge upon such walls. Furthermore, particles adhering to the well bottom cannot be examined with a microscope having powerful objectives, since the objectives cannot be positioned sufficiently close to the bottom of the well because of interference from the walls. Also, it often is difficult to deposit a non-reacting "control" in a microwell with the intention of monitoring that control.
Still another disadvantage found in the use of conventional microtitration plates resides in the need to introduce freshly prepared reagents into the microwells for analysis. It has heretofore generally been difficult, if not impractical, to store previously prepared, dry reagents in such microwells for subsequent activation by the introduction therein of water or water-containing samples for reaction therewith.